Influence of Interaction Between Qubits on Entanglement Sudden Death and Birth

Dynamic evolution of entanglement is studied for coupling two-qubit system in non-Markov environment in terms of concurrence. We find that the degree of entanglement depends on the initial quantum state of the system and the interaction between the two-qubit system and the environment. When the interaction between the qubits and the environment is completely symmetric, especially, the environment has no effect on the entanglement, where the decoherence is entirely resulted from the interaction between qubits. By controlling the coupling way of the interaction, thus, one may avoid the entanglement sudden death (ESD).     

Sudden Death and Long-Lived Entanglement Between Two Atoms in a Double JC Model System

Considering a double JC model with different coupling constants, we investigate the entanglement between the two two-level atoms, and discuss dependence of the atom-atom entanglement on the different coupling constants, and the detuning between the atomic transition frequency and the cavity field frequency. The results show when Δ=δ/g is small, with the increase of the relative difference of the two atom-cavity coupling constants γ, the atom-atom entanglement periodically evolves with the amplitude slowly and periodically modulated. What’s more interesting is that long-lived entanglement between the two atoms can be obtained when atom A non-resonantly interacts with the cavity field a, and atom B has no coupling with the cavity field b. In this case, the concurrence C ^AB (t) of the two atoms evolves in form of cosine, and is invariant and equals the initial value when far off resonance. In addition, we find that the so-called entanglement sudden death can occur under appropriate conditions on the detunings and the different coupling constants for different initial atomic states.     

Entanglement Sudden Death in Quantum Optics： What is it and why does it happen？

It is well known in quantum optics that fluctuations and dissipation inevitably intervene in the dynamics of open quantum systems. Density matrix elements may all decay exponentially and smoothly but we show that two-party entanglement, a valuable quantum coherence, may nevertheless abruptly decrease to zero in a finite time. This is Entanglement Sudden Death. In this talk we show how entanglement sudden death occurs under either phase or amplitude noise, either quantum or classical in origin. Moreover, we show that when two or more noises are active at the same time, the effects of the combined noises is even more unexpected.     

Entanglement Transfer and Periodic Sudden Death Phenomenon in Two Parallel 1D Spin Chains of Quantum Spin Network

We investigate the entanglement transfer in two parallel ID spin chains of a quantum spin network, and show that the perfect entanglement transfer can be realized at some special times. In addition, the so-called ＇sudden death＇ phenomenon of entanglement is found in the spin network system.